Production of disulfides



Patented Apr. 27, 1954 PRODUCTION OF DISULFIDES Willie W. Crouch and Robert T. Werkman, Bartlesville, kla., assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application January 2, 1951, Serial No. 204,061

1 This invention relates to the production of bis(alkylmercaptothiocarbonyl) one of its specific aspects it relates to the production of bis(alkylmercaptothiocarbonyl) disulfides by oxidation of metal salts of alkyl trithiocarbonic acids. More specifically, this invention relates to the production of bis alkylmercaptothiocarbonyl) disulfides by oxidizing a water dispersion of a salt of a trithiocarbonic acid using an alkali metal hypochlorite as the oxidant. In one specific embodiment, our invention relates to a particularly advantageous method for producing bis(alkylmercaptothiocarbonyl) disulfides comprising the rapid addition of oxidant to the salt of the trithiocarbonic acid.

The art teaches several methods for the production of compounds including bis(alkylmercaptothiocarbonyl) disulfides, all of which disulfides. In

13 Claims. (Cl. 260-455) processes we have found to be unsatisfactory,

either for the reason that the yield of desired compound is small or undue quantities of side reaction products are obtained. For instance, one method is to use as the oxidant chlorine gas, however, when producing the his(alkylmercaptothiocarbonyl) disulfides of this invention, we have found the yields to be much less than desirable.

An object of this invention is to provide an improved method for producing bis(alkylmercaptothiocarbonyl) disulfides.

Another object of this invention is to provide a method for the production of bis(alkylmercaptothiocarbonyl) disulfides whereby the yields of product are considerably greater than those obtained by prior art methods.

- Another object of this invention is to increase the ratios of bis(alkylmercaptothiocarbonyl) disulfide product to side reaction products.

Other objects and advantages will be apparent to those skilled in the art from the accompanying discussion and disclosure.

- We have discovered an improved process for the production and increased yields of bis(alkylmercaptothiocarbonyl) disulfides obtained by the oxidation of metal salts of alkyl trithiocarbonic acids with alkali metal hypochlorites. Broadly, our invention comprises the rapid addition of the oxidizing agent to the material to be oxidized with efficient agitation. We have found that any reduction in mixing time improves the yields of his(alkylmercaptothiocarbonyl) disulfides obtained. We generally prefer, however, to cause the admixing of oxidant and material to be oxidized to take place as rapidly as possible. Additional improvement in overall quantity of prodwe have found that by actually dumping the total quantity of oxidant necessary into the salt of the trithiocarbonic acid, improved results are obtained over those provided by other slower methods of addition. The more rapid the addition of oxidant to the salt to be converted to a bis(alkylmercaptothiocarbonyl) disulfide, the greater is the quantity of desired product and, concomitantly, the smaller is the quantity of undesirable byproduct, an oily material formed by side reactions. Thus, if a 30 minute period is used to add the oxidant by prior art methods, we have found that a reduction to 15 minutes in the addition time is advantageous. Going still further, we have found that even more rapid addition is of great advantage, and We generally prefer to admix the material to be oxidized and the oxidant in a time at least as short as 3 minutes and generally within one minute or less, such as within 30 seconds. To accomplish such rapid admixture, large reactors and the like are npt very desirable. Weprefer that mixing take place in mixing tees, venturis, and similar equipment. We do not, however, exclude the use of large chambers for settling or for completion of the oxidation reaction, but we do prefer the use of equipment which will provide the most rapid mixing possible. The temperature ranges within which we prefer to work are 0 to F.. and preferably 25 to 50 F. When operating at the low temperatures, freezing point depressants which are not affected under conditions of the reaction, such as acetone, can be employed if desired or necessary.

The oxidation reaction of the salts of alkyl trithiocarbonic acids to give bis(alkylmercaptothiocarbonyl) disulfides takes place according to the following equation:

s s 2Iist sM MOOl H1O (EN IS): +2MOH +Mol where R represents an alkyl radical and M is an alkali metal. It is to be noted that in our process the salt of the alkyl trithiocarbonic acid centration of to 30 weight per cent.

reacts at the sulfur atom connected to the alkali metal, and not at the alkyl group. Thus, the alkyl group does not serve as a functional group. The term alkyl is used here broadly and is not to be interpreted to limit applicants merely to a group which is entirely aliphatic or hydrocarbon in nature. We mean to include in addition to purely unsubstituted alkyl hydrocarbons, those hydrocarbons containing ether or thioether linkages, cycloalkyl groups, alkyl groups containing aromatic rings substituted for hydrogen atoms thereon, or groups containing elements or radicals inert to the oxidation reaction.

The aqueous solution or dispersion of the alkyl trithiocarbonate to be oxidized is made up by dispersing or dissolving a solid or crystalline alkali metal salt of an alkyl trithiocarbonic acid in Water. Alternatively, the solution may be made up by reacting an allrali metal hydroxide such as sodium hydroxide with carbon disulfide and an alkyl mercaptan in water according to the equation:

s use! cs1 NaOH ss o sna -ngo where R is an alkyl radical containing 1 to 12 carbon atoms.

Still another method of procedure is to prepare the salt of the alkyl trithiocarbonic acid in a non-aqueous diluent as described in copending application, Serial No. 783,830, filed November 3. 1947, now Patent No. 2,600,737. In this application a slurry of the alkali metal salt of the alkyl trithiocarbonic acid the diluent is formed. This slurry is then added rapidly to a dilute aqueous alkali metal hypochl rite solution. In this case the aqueous solution of the alkali metal salt of the allzyl trithiocarbonic acid is produced in situ when the slurry is added to the aqueous hypochlorite, i. e., the trithiocarbonate goes from the hydrocarbon phase to the aqueous phase. The product of the reaction is then dissolved as it is formed in the non-aqueous phase. We have found this mode of operation particularly well suited to continuous operation.

In carrying out the process of our invention, an alkali metal salt of an alkyl trithiocarbonic acid is used containing from 1 to 12 carbon atoms in the alkyl group and also containing an alkali metal such as sodium, potassium, or lithium.

Suitable salts of alkyl trithiocarbonic acids which can be used are exemplified by the following: potassium tertiary octyl trithiocarbonate, sodium secondary propyl trithiocarbonate, sodium primary dodecyl trithiocarbonate, sodium tertiary butyl trithiocarbonate, and sodium cyclohexyl trithiocarbonate. The concentration of the trithioearbonate is 50 weight per cent or less of the solution or dispersion and is. preferably in the range of 10 to to weight per cent of the solution or dispersion. We have obtained very satisfactory results using the trithiocarbonate in a con- The alkali rnetal hypochlorite solution employed as oxidant can be of a concentration in the range of 0.3 to 40 weight per cent, however, we usually prefer the range of 1 to weight per cent. In some cases both the concentration of the trithiocarbonate and the hypochlorite may vary outside these ranges, however, generally speaking, these ranges are those preferred.

We have found that operating by the prior art method of bubbling chlorine into a basic solution to prepare a disulfide of the type disclosed herein is not equivalent to using an aqueous solution of an alkali metal hypochlorite, even though bubbling chlorine into an aqueous alkaline solution results in the formation of a hypochlorite. When using chlorine as the oxidant, We have found that practically none of the desired product is obtained.

Advantages of this invention are illustrated by the following examples. The reactantsv and their proportions, and other specific ingredients are presented as being typical and should not be construed to limit the invention unduly.

Ezrample I To a stirred solution of grams of sodium tertiary butyl trithiocarbonate dihydrate dissolved in 400 ml. of water were added 450 ml. of 5.25 weight per cent aqueous solution of sodium hypochlorite. All of the sodium hypochlorite solution was poured in at one time. The reaction, i. e., the oxidation of the sodium tertiary butyl trithiocarbonate dihydrate, was effected at a temperature of 35 F. and was completed rapidly. The crude product was recovered and purified by recrystallizing bis(tertbuty1mercaptothiocarbonyl) disulrlde. A yield of 81 per cent of theoretical of this purified product was obtained, while only 13 grams of oily by-products were recovered.

Example I I In a run similar to that of Example I, the hypochlorite solution was added to the sodium tertiary butyl trithiocarbonate dihydrate over a period of 30 minutes. The yield of purified crystalline bis(tert-butylmercaptothiooarbonyl) disulfide was only 26.5 per cent of theoretical, while 11 grams of oily icy-products were obtained.

A comparison of this example with Example I shows the tremendous improvement in product yield obtained by the rapid addition of the oxidant to the material to be oxidized. It also shows the decrease in ratio of lay-products to product.

Example III To 50 grams of sodium tertiary butyl trithiocarbonate dihydrate dissolved in water to make a solution of about 30 weight per cent concentration was added a 5.25 Weight per cent solution of sodium hypochlorite at a rate of about 7 ml. per minute. As the sodium hypochlorite was added, a viscous, reddish-brown oil separated from the solution. Addition of the oxidant was continued until no further separation of oil was observed. The reaction product was then recovered, dissolved in methanol, and crystallized by cooling in a Dry Ice bath to give a yellow, crystalline material. After two more recrystallizations from methanol, the product, bis(tertbutylmercaptothiocarbonyl) disulfide, had a melting point of to 135 F. The sulfur content was 57.7 per cent compared to the theoreti cal value of 53.1 per cent for this compound. The solid disulfide was readily soluble in diethyl ether, pentane, toluene, acetone, and methanol. and was insoluble in water.

The preceding oxidation was efiected at a temperature of 70 F., and the yield of the desired crystalline product, based on the weight of sodium tertiary butyl trithiocarbonate, was only 30 per cent of theoretical, 01' 11 grams, while 9 grams of oily by-product was formed. By a similar oxidation carried out at a temperature of 35 F. instead of 70 the yield of the desired crystalline disulfide was raised to 43 per cent of theoretical.

Example IV A series of oxidations was efiected using varying amounts of oxidant. These runs were also carried out using rapid mixing of the reactants, but they difiered from Example I in that the trithiocarbonate solutions were poured rapidly into the stirred sodium hypochlorite solutions. The reaction temperature in each case was 35 F. In each case the trithioearbonate solution to be oxidized was made by dissolving 40- grams of sodium tertiary butyl trithiocarbonate dihydrate in about 200 ml. of water. The sodium hypochlorite solutions in each instance were 1.75 weight per cent concentration. The table shows the amount of oxidant used and the yields obtained.

1 Percent of theoretical, based on weight of trithiocarbonate used.

These results indicate that under the conditions employed an excess of the oxidant is required for best yields.

Example V This example is included merely to show the efiectiveness of chlorine as compared with the oxidant employed in the invention.

Chlorine gas was passed for two hours through an aqueous solution containing 30 grams of sodium tertiary butyl trithiocarbonate. A low yield, less than 5 grams, of a mixture of a yellow solid and a lesser amount of oil was obtained. The solid was identified as free sulfur.

As will be evident to those skilled in the art, various modifications of this invention can be followed in the light of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

We claim:

1. A method for preparing bis(alkylmercaptothiocarbonyl) disulfides, which comprises oxidizing an alkali metal salt of an alkyl trithiocarbonic acid wherein the alkyl group contains from 1 to 12 carbon atoms with an alkali metal hypochlorite, carrying out said oxidation such that said salt of an alkyl trithiocarbonic acid and said alkali metal hypochlorite are admixed rapidly.

2. A method according to claim 1 wherein the admixing is carried out within three minutes.

3. A method for preparing bis(alkylmercaptothiocarbonyl) disulfides, which comprises oxidizing an alkali metal salt of an alkyl trithiocarbonic acid wherein the alkyl group contains from 1 to 12 carbon atoms with an alkali metal hypochlorite at a temperature in the range of 0 to 70 F., carrying out said oxidation such that said salt and said ypochlorite are admixed within three minutes.

4. A method for preparing bis alkylmercaptothiocarbonyl) disulfides, which comprises oxidizing an alkali metal salt of an alkyl trithiocarbonic acid wherein the alkyl group contains from 1 to 12 carbon atoms with an alkali metal hypochlorite, said salt of an alkyl trithiocarbonic acid containing 1 to 12 carbon atoms in the alkyl group, utilizing to 140 weight per cent of the theoretical quantity of hypochlorite necessary to react with said salt of an alkyl trithiocarbonic acid, and carrying out said oxidation such that said salt of an alkyl trithiocarbonic acid and. said alkali metal hypochlorite are admixed within three minutes, and at a temperature in the range of 0 to 70 F.

5. In a method according to claim 4, carrying out said reaction at a temperature in the range of 25 to 50 F.

6. In a method according to claim 4, wherein a freezing point depressant inert to the reaction is admixed with the reactants.

7. A method according to claim 4 wherein said salt of an alkyl trithiocarbonic acid is utilized in an aqueous solution containing not more than 50 weight per cent of said salt.

8. A method according to claim 4 wherein said salt of the alkyl trithiocarbonic acid is employed as a non-aqueous slurry, said salt comprising not more than 50 Weight per cent of said slurry.

9. A method for preparing bis(alkylmercaptothiocarbonyl) disulfides, which comprises oxidizing not more than a 50 weight per cent aqueous solution of an alkali metal salt of an alkyl trithiocarbonic acid wherein the alkyl group contains from 1 to 12 carbon atoms with 100 to 140 weight per cent of the theoretical quantity of an alkali metal hypochlorite in aqueous solution at a temperature in the range of 25 to 50 F. and admixing said salt and said hypochlorit in not more than one minute.

10. A method according to claim 9 wherein to weight per cent of the theoretical quantity of hypochlorite is used.

11. A method according to claim 9 wherein said hypochlorite is used in a 0.3 to 40 weight per cent aqueous solution.

12. A method according to claim 9 wherein said hypochlorite is used in a 1 to 20 weight per cent aqueous solution.

13. A method for preparing bis(tert-butylmercaptothiocarbonyl) disulfides, which comprises rapidly admixing an aqueous solution of sodium tertiary butyl trithiocarbonate dihydrate with 5.25 weight per cent of an aqueous solution of sodium hypochlorite, dumping all of said sodium hypochlorite solution into said sodium tertiary butyl trithiccarbonate solution at one time, carrying out the oxidation at a temperature of about 35 F., recovering bis(tert-butylmercaptothiocarbonyl) disulfide by recrystallization, and obtaining a yield of about 81 per cent of theoretical of a purified product.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,832,163 Whitby Nov. 17, 1931 2,021,726 Hess Nov. 19, 1935 2,268,382 Cloud Dec. 30, 1941 2,270,257 Browning Jan. 20, 1942 2,453,689 Beaver Nov. 16, 1948 OTHER REFERENCES Beaver et al., Rubber Chemistry and Technology (1944), vol. 17, pages 896-902. 

3. A METHOD FOR PREPARING BIS(ALKYLMERICAPTOTHIOCARBONYL) DISULFIES, WHICH COMPRISES OXIDIZING AN ALKALI METAL SALT OF AN LAKYL TRITHIOCARBONIC ACID WHEREIN THE ALKYL GROUP CONTAINS FROM 1 TO 12 CARBONS ATOMS WITH AN ALKALI METAL HYPOCHLORITE AT A TEMPERATURE IN THE RANGE OF 0 TO 70* F., CARRYING OUT SAID OXIDIATION SUCH THAT SAID SALT AND SAID HYPOCHLORITE ARE ADMIXED WITHIN THREE MINUTES. 